There has heretofore been known a device, for detecting hydrogen concentration, which utilizes the fact that the thermal conductivity of hydrogen is higher than that of the air.
For example, a hydrogen concentration detecting device disclosed in JP-A-2003-130834 detects hydrogen concentration based on a difference in the change of resistance between a detector element and a reference element both of which containing a thermistor therein.
According to the hydrogen concentration detecting device disclosed in JP-A-2003-130834, however, a flow of gas such as the air or hydrogen around the detector element robs heat from the detector element causing a variation in the resistance thereof. Therefore, the value that is detected tends to be higher than the real hydrogen concentration.